A flat panel display (FPD) that utilizes an optical film (e.g., polarizer and retardation film) can achieve high-resolution display, and has been widely used as an advantageous display device.
Examples of the retardation film include a quarter-wave plate that converts linearly polarized light into circularly polarized light, a half-wave plate that converts the plane of vibration of linearly polarized light by 90°, and the like. These retardation films can achieve accurate conversion of specific monochromatic light so that ¼λ or ½λ retardation occurs.
However, known retardation films have a problem in that polarized light that passes through is converted into colored polarized light. Specifically, since a material that forms the retardation film has wavelength dispersion with respect to retardation, and a polarization state distribution corresponding to each wavelength occurs with respect to white light that includes different light beams in the visible region, it is impossible to achieve accurate ¼λ or ½λ retardation over the entire wavelength band.
In order to solve the above problem, various wideband retardation films that can achieve uniform retardation with respect to light over a wide wavelength band (i.e., retardation films having reverse wavelength dispersion) have been studied (see Patent Documents 1 to 6, for example).
It has been desired to reduce the thickness of the flat panel display as much as possible along with an improvement in performance and widespread use of mobile information terminals (e.g., mobile personal computer and mobile phone). Therefore, a reduction in thickness of the retardation film has also been desired.